1. Field of the Art
This invention relates to a control apparatus for a power converter, and more particularly to an apparatus for controlling a power converter, e.g., a PWM inverter for an uninterruptible power supply, a static var compensator, an active filter, etc. by making use of learning control.
2. Prior Art
For a control system for a power converter which can attain high speed response, "Deadbeat Control System" is proposed ("Deadbeat Microprocessor Control of PWM Inverter for Sinusoidal Output Waveform Synthesis" PESC '85 Conference Record, 1985).
However, even with high speed response as in such a deadbeat system, it is still difficult to control the output voltage with loads such as a capacitor input load, a phase-controlled rectifier load, or the like so that the output distortion factor becomes sufficiently small. This is because if a correcting action is made only after a rise or dip due to each sudden load change of the cyclic load fluctuation, the correcting action never compensates the rise or dip already occurred.
Meanwhile, in "Waveform Compensation of PWM Inverter with Cyclic Fluctuating Loads" (IAS '86 Conference Record, 1986), it is reported that an application of a repetitive control to a PWM inverter having a rectifier load results in a very low distortion factor of the output voltage. In general, control method, including the repetitive control, which stores variables of a main circuit or a control circuit over a fixed time period and utilizes the stored values for a subsequent control, is called "Learning Control".
While the above-mentioned learning control is a very effective control method, it has the following problems. In an actual power converter, abnormal states such as load short-circuiting, overload, overvoltage, undervoltage, etc. may occur. If writing into the memory is simply continued during occurrence of an abnormal state as well, an abnormal value or values stored in the memory are to be erroneously utilized after the abnormal state ends and the normal operation restarts. As a result, waveforms after the restart will deviate.